When sulfur is removed from petroleum, hydrogen sulfide (H2S) gas is often produced. This gas can oxidize to sulfur and ultimately to sulfur dioxide (SO2). It is important to remove sulfur from petroleum products in order to reduce SO2 emission during combustion in automotive vehicles, aircraft, locomotives, ships, gas or oil burning power plants, residential and industrial furnaces, etc., thus reducing negative environmental effects, such as acid rain. Sulfur is also removed from the naphtha streams within a petroleum refinery because, even in extremely low concentrations, sulfur poisons the noble metal catalysts (e.g., platinum and rhenium) that are used to upgrade the octane rating in the catalytic reforming units.
Of particular concern is the removal of H2S from hydrotreated products. If dissolved H2S is not removed from the hydrotreated product before the product is exposed to air, the product's sulfur content count increases due to oxidation of H2S to elemental sulfur. This interference prohibits the determination of accurate product sulfur values for ultra low sulfur diesel (ULSD) studies, where the target product sulfur is typically below about 10 ppm.
U.S. Pat. No. 3,984,316 describes a process for removing dissolved H2S from refinery waste water using a countercurrent stream of an absorber gas, which can comprise, among other things, nitrogen. U.S. '316 fails to describe treating a hydrotreated product and does not disclose packing a column with inert material, such as glass beads.
U.S. Pat. No. 7,361,625 addresses the photocatalytic removal of volatile organic compounds (VOCs) and unwanted gases from cracked olefin streams. U.S. Pat. No. 7,361,625 describes a process for the hydrodesulfurization of a cracked olefin stream wherein a mixture of H2 and an inert gas, for example N2, CH4, C2H6, C3H8, C4H10, or noble gases (e.g., He, Ar), are mixed with the olefin stream. The mixture is heated and contacted with a desulfurization catalyst. As desulfurization occurs, the resulting H2S is removed using the H2—N2 gas stream.
Broderius and Smith (“Direct determination and calculation of aqueous hydrogen sulfide”, Anal. Chem., 1977, 49 (3), pp 424-428) describe measuring the concentration of hydrogen sulfide in water. The aqueous H2S solution is sparged with nitrogen to displace the H2S gas. The displaced H2S gas is collected in a glass bed concentration column and measured colormetrically.
Sakanishi et al. (“Removal of Hydrogen Sulfide and Carbonyl Sulfide for Purification of Biomass Gasified Synthetic Gas Using Active Carbons”, Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem., 2004, 49(2), 580) describe adsorption rates of H2S from a gas mixture consisting of H2S and N2. Columns are packed with glass beads, and adsorptions are measured at variable temperatures.
Generally, dissolved H2S is scrubbed from petroleum products in situ with a caustic wash solution. Because H2S is considered a weak acid gas, its scrubbing calls for a strong alkali, such as NaOH, with caustic soda to accomplish in this method. This process, however, requires elaborate sample preparation, is very time-consuming, costly, exposes and endangers technicians to the risk of caustic solutions, and is impractical for denser and higher boiling point hydrocarbons.
What is needed in the art are better, more cost effective, and safer ways of removing H2S from refinery streams, and especially from hydrotreated products.